Field of the Invention
The present invention relates to wireless communication, and more particularly, to an asynchronous Direct Link Setup (DLS) scheme in which a channel bandwidth is divided and frames are independently transmitted in the divided bandwidths between DLS connection and non-DLS connection in a Wireless Local Access Network (WLAN) system.
Discussion of Related Art
With the development of the information communication technology, various wireless communication technologies are being developed. From among them, the WLAN technology has been developed to wirelessly access the Internet in specific service areas, such as homes, companies, and aircraft, using portable terminals, such as Personal Digital Assistants (PDAs), laptop computers, and Portable Multimedia Players (PMPs) based on the wireless frequency technology.
The WLAN technology at the early stage was developed to support the 1 to 2 Mbps speed through frequency hopping, band spreading, and infrared communication using a frequency of 2.4 GHz through IEEE 802.11. With the recent development of the wireless communication technology, an Orthogonal Frequency Division Multiplexing (OFDM) technology, etc. is applied to the WLAN technology in order to support a maximum speed of 54 Mbps. In addition, in IEEE 802.11, wireless communication technologies for the improvement of Quality of Service (QoS), an Access Point (AP) protocol compatibility, security enhancement, radio resource measurement, wireless access in vehicular environments, fast roaming, a mesh network, inter-working with an external network, and wireless network management have been developed and commercialized or are being developed.
In IEEE 802.11, a Basic Service Set (BSS) refers to a set of STAs which are successfully synchronized, and a Basic Service Area (BSA) refers to an area including members constituting a BSS. The BSA may be changed depending on the propagation characteristic of a wireless medium, and so it has an obscure boundary. The BSS may be basically classified into an Independent BSS (IBSS) and an Infrastructured BSS. The independent BSS forms a self-contained network and refers to a BSS which is not permitted to access a Distribution System (DS). The infrastructured BSS includes one or more APs, DSs, etc. and chiefly refers to a BSS in which the APs are used in all communication processes including communication between STAtions (STAs).
In accordance with the early WLAN communication procedure, in the infrastructured BSS, it was required that the direction transmission of data between non-AP STAs be not permitted, but data be transmitted via an AP. Recently, to improve the efficiency of wireless communication, DLS between non-AP STAs is supported. In this technology, in a BSS supporting QoS (i.e., a Quality of Service BSS (QBSS) composed of a QSTA and a QAP), non-AP stations may set up a direct link and directly communicate with each other through the direct link even without passing through the QAP.
Meanwhile, with the spread of a WLAN being activated and applications using the WLAN being diversified, there is an emerging need for a new WLAN system capable of supporting a higher throughput than the data processing speed supported by IEEE 802.11n. However, an IEEE 802.11n Medium Access Control (MAC)/Physical Layer (PHY) protocol is not effective in providing the throughput of 1 Gbps or more. This is because the IEEE 802.11n MAC/PHY protocol is for the operation of a single STA (i.e., an STA having one Network Interface Card (NIC) and so overhead is added with an increase in the throughput of frames with the existing IEEE 802.11n MAC/PHY protocol remained intact. Consequently, there is a limit to the improvement of the throughput of a wireless communication network with the existing IEEE 802.11n MAC/PHY protocol (i.e., a single STA architecture) remained intact.
Accordingly, to achieve the data processing speed of 1 Gbps or more in a wireless communication network, there is a need for a new system different from the IEEE 802.11n MAC/PHY protocol (i.e., the existing single STA architecture). A Very High Throughput (VHT) WLAN system is the next version of the IEEE 802.11n WLAN system and is one of IEEE 802.11 WLAN systems which are recently newly proposed in order to support the data processing speed of 1 Gbps or more in a MAC Service Access Point (SAP).
The VHT WLAN system allows a plurality of VHT STAs to simultaneously access and use a radio channel so as to efficiently use radio channels. To this end, the VHT WLAN system supports the transmission of a Multi-User Multiple Input Multiple Output (MU-MIMO) method using multiple antennas. A VHT AP may perform a Spatial Division Multiple Access (SDMA) transmission method of transmitting spatial multiplexed data to a plurality of VHT STAs.
In the case in which DLS is used, a throughput gain through SDMA transmission between an AP and an STA may not be obtained because transmission using SDMA may not be simultaneously performed between the AP and the STA. In the case in which a direct link is set up between STAs and transmission and reception are performed therebetween, a method of performing transmission using SDMA between an AP and an STA and an STA supporting the method need to be taken into consideration.